In the field of nuclear physics research, many devices produce a large flux of neutrons within a period of a few microseconds. Examples of such devices are burst reactors, atomic and thermonuclear bombs, accelerators, and excursions of critical masses of fissionable material in reprocessing plants used to separate fissionable isotopes from spent fuel elements. It is often necessary to trigger equipment such as cameras, sensors, alarms or relays at a time extremely soon after such devices emit a burst of neutron radiation.
Other radiations are typically associated with the production of neutrons from such devices. These other radiations may include gamma rays, beta particles and electromagnetic radiation. Often, these radiations will activate competing reactions in detectors used to measure neutron emission. These competing reactions can limit the usefulness of those detectors.
In laboratory and plant environments it is very important to be able to detect the emission of neutrons by a material and produce an alarm in the shortest possible time. For example, neutron detection is important for personnel protection during the reprocessing of spent fuel rods removed from nuclear reactors.
Although there are numerous commercial neutron detectors available, many are not sufficiently fast to allow experimenters to conduct certain experiments. Neutron detectors that require relays to operate ancillary equipment require approximately 0.01 sec to operate. This amount of time can be too long for some experimental applications, where most events associated with the experiments would be over before the relay closed.
The present invention solves these problems by providing apparatus which has the ability to discriminate against gamma and other competing radiations, and to respond to neutron radiation. It also responds within microseconds, much faster than conventional relays which require 0.01 seconds when actuated by currents from ion chambers or photo tubes.
The invention is capable of this performance because it directly utilizes the neutron burst to produce fissions in an active element constructed of a fissionable material. The fission fragment energy is converted to heat by collisions in the active element. Metals respond almost instantaneously to heat energy and convert the heat to a change in dimension. The heating of the active element by fission is orders of magnitude greater than that produced by other radiations. This fact provides the discrimination against deleterious effects from such other radiations.
It is therefore an object of the present invention to provide a switch capable of closing within a few microseconds after bombardment by a large flux of neutrons.
It is a further object of the present invention to provide a fast reacting neutron activated switch which discriminates against other radiations which may be present in the neutron flux.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.